The present invention generally relates to a clock system which corrects the present time automatically using a time transmitted from a satellite, and more particularly to a clock system which receives signals at a fixed place on Earth always from the same satellite, thereby maintaining the present time with high accuracy.
A conventional clock system, which corrects automatically the time using a time data transmitted from a satellite, is disclosed in the Japanese Patent Application Non-Examined Publication No. H10-10251. This is known as an electronic clock system. This electronic clock system receives a high-frequency signal in L1 band (approx. 2 MHz bandwidth on 1575.42 MHz) transmitted from a Global Positioning System (GPS) satellite to the system""s antenna. The received high-frequency signal is converted to an intermediate frequency. Then the intermediate frequency signal is multiplied by a code unique to the GPS satellite which is to be locked on, and synchronised with the signal transmitted from the satellite, and the data is thus decoded. Since the decoded data includes the time data, a GPS time (the time when the satellite transmits the signal) is found out of the time data. The coordinated universal time (hereinafter referred to as xe2x80x9cUTCxe2x80x9d) is acquired by converting the GPS time.
A local time of a region, where the clock system is used, can be found from the UTC, because a time difference from the UTC has been stored in a memory, e.g. a ROM. However, this conventional clock system using the GPS satellite has the following problems: Since the GPS satellites are orbiting, a fixed point on Earth is obliged to receive a signal from a different GPS satellite depending on a time slot, therefore, at the local region, a receivable GPS satellite should be predicted, or a plurality of channels are prepared in the receiving system. Further, at a particular place, no GPS satellite can be received depending on the time slot, and thus this place cannot keep accurate time.
The present invention addresses the problems discussed above and aims to provide a clock system, which receives a signal at a fixed point on Earth always from the same satellite, so that the system can keep time with high accuracy.
The present invention thus concerns a clock system as defined in the appended claims.
This clock system comprises the following elements:
(a) a receiver for receiving a signal transmitted from a stationary satellite;
(b) a calculator for extracting time data from a received signal and calculating the time;
(c) a memory for storing correction information used in converting the stationary satellite time into UTC;
(d) a clock circuit; and
(e) a display.
The time of the clock circuit is corrected by the time calculated by the calculator, and then displayed on the display. This structure allows any local fixed place on Earth to receive a time data always from the same satellite, thereby keeping highly accurate time.